The conventional mechanical fuel pump computer incorporates a mechanical register having a pair of counters on each of two opposite faces of the register (with each counter having a bank of four or five coaxial rotary number wheels) for registering on each of the opposite faces of the register, the cost and volume amounts of fuel dispensed. Such a register is disclosed in the aforementioned U.S. Pat. No. 2,814,444.
The conventional mechanical fuel pump computer also incorporates a mechanical variator for establishing and posting the unit volume price of fuel. Such a mechanical variator is disclosed in U.S. Pat. No. 4,136,573 of Bruno S. Smilgys et al, dated Jan. 30, 1979 and entitled "Extended Range Variator Conversion Mechanism". The variator disclosed in U.S. Pat. No. 4,136,573 provides for establishing and posting a unit volume price within a range of 0000 to 2999, and in a modified form of that variator disclosed in pending U.S. patent application Ser. No. 259,708 of Raymond H. Devanney, filed May 1, 1981, entitled "Extended Range Variator Conversion Mechanism", and assigned to the assignee of the present application, the variator is operable for establishing and posting a unit volume price within an extended range of 0000 to 5999.
In the conventional mechanical computer installation, the mechanical computer is mechanically driven by a suitable fuel meter for registering the volume amount of fuel delivered (conventionally in gallons in the U.S.A. and in liters in the U.K.) and the cost amount of fuel delivered in accordance with the volume amount delivered and the unit volume price established by the variator setting. In such an installation, the mechanical computer will normally have a long, maintenance free useful life if the rotational speeds of the computer parts are held within acceptable limits. The recommended maximum operating speed of the mechanical computer is usually given as a recommended maximum operating speed of the right hand or lowest order number wheels of the computer. Such a maximum operating speed is preferably about 150 revolutions per minute (rpm) but may be established as high as 200 or even 250 rpm. In any event, the mechanical computer is preferably operated at the lowest practical speed to extend its useful life.
The normal maximum fuel delivery rate of a conventional fuel dispenser is typically approximately 15 gallons per minute in the U.S.A. and 50 liters per minute in the U.K. Also, in the conventional fuel dispenser the right hand number wheels of both the cost and volume counters are single transfer, 10 value wheels marked 0-9 for recording a value of ten for each revolution. Thus, with a maximum right hand number wheel speed of 150 rpm and 10 value right hand number wheels, the maximum cost rate of delivery is $15.00 a minute in the U.S.A. (where the right hand cost counter wheel is used to register the cents amount of fuel dispensed) and the maximum gallon unit volume price is $1.00 (i.e. $15.00/minute.div.15 gallons/minute). In the United Kingdom, where the right hand cost counter wheel is used to register the pence amount of fuel dispensed and the maximum fuel delivery rate is 50 liters per minute, the maximum unit volume price is 30 pence per liter with a maximum wheel speed of 150 rpm.
In the U.S.A. and U.K. and in other countries using other currencies and having an inflation rate which is often higher than that in the U.S.A. and U.K., the speed of the right hand cost counter wheels has been reduced by increasing their value. For example, conversion of the mechanical computer to replace the conventional 10 value right hand cost counter wheels with 20 value wheels enables the cost counter drive ratio to be reduced by a factor of two and provides a cost indicating rate of 3,000 per minute, thereby permitting for example a maximum unit volume price of 60 pence per liter in the U.K. and $2.00 a gallon in the U.S.A. without exceeding a right hand number wheel speed of 150 rpm.
Because of the escalating unit volume price of fuel and the resulting increasing rate of rotation of the right hand number wheels of the register cost counters for any given maximum volume rate of fuel dispensed, the conventional 10 value or single transfer right hand cost counter wheel has in some instances been replaced by a multiple transfer wheel (e.g. a 20 value or double transfer wheel or a 40 value or four transfer wheel) or by a 100 value, single transfer wheel to reduce the rate of rotation, required drive torque and rate of wear of the cost counters. When the value of the right hand cost counter wheels are changed, for example by substituting 20 value double transfer wheels for 10 value, single transfer wheels, modification of the drive train to the mechanical cost counters is required so that the rate of rotation of the right hand cost counter wheels is reduced by the same factor that it is increased in value. As a result, for any given unit volume price setting of the variator, the right hand cost counter wheels accumulate the cost amount of fuel dispensed at the same cost rate but at a lower rotational speed.
In order to overcome the money wheel speed problem in any particular country, the rotational speed of the right hand cost counter wheels can be reduced as described above where that is a practical solution within the constraints imposed by the pricing requirements and practices of that country. However, it may become necessary or desirable to change the right hand cost counter wheels and cost counter drive ratio to reduce the number wheel operating speed by one factor in one country and by a different factor in a different country.
In the usual mechanical computer installation, the right hand or lowest order volume counter wheels conventionally are unit volume wheels (i.e. rotate one revolution for each unit volume of gasoline dispensed) and are generally readable only to the nearest one-tenth unit volume of fuel dispensed. Accordingly, the calculated cost determined by multiplying the volume counter readout and the unit volume price established by the variator setting is conventionally accurate for example only to the nearest $0.005 at a unit volume price of $1.00 and to the nearest $0.025 at a unit volume price of $5.00. As a result, it is becoming more and more important to read the volume counters to the nearest one-hundredth unit volume to provide greater correspondence between the calculated cost and the cost displayed by the cost counters. Such can be accomplished by increasing the volume counter drive ratio by a factor of ten, in effect to shift the volume counter decimal point one place to the left. However, because of the resulting higher right hand wheel speed and lower maximum volume readout, the volume counter drive ratio is preferably changed only when such becomes necessary as a result of the escalating unit volume price.
From a manufacturing and repair standpoint, it is highly desirable to use the same mechanical computer configuration throughout the world and without structural modification of the computer. Such flexibility is difficult to achieve particularly because of the varying local requirements, standards and practices regarding the unit volume measure to be used and the least significant digit to which the unit volume price in the local currency is to be set, posted and registered by the mechanical computer. For example, in the U.S.A., the gallon is the standard unit volume on which gasoline is priced and gasoline continues to be priced to the nearest one-tenth cent even to where fuel is now priced to four places to the nearest one-tenth cent. Also, in most countries, the oil companies continue to prefer to price fuel to the smallest possible increment primarily for purposes of price competition.
There is no real problem in replacing the right hand cost counter wheels (e.g. to substitute a 20 value, double transfer wheel for a 10 value, single transfer wheel) since such wheel replacement can be done without removing the computer from the pump and therefore at a relatively low cost. However, in the conventional mechanical computer, it is expensive to change the volume counter drive ratio or to change the cost counter drive ratio when the cost counter wheels are replaced as such typically requires removing the computer from the pump and separating the register from the variator to modify the counter drive train gearing.